Relay



Jam 2, 1962 G. E. PERREAULT 3,015,707

RELAY Filed Nov. 19, 1957 SHIFT DUE T0 PERMANENT MAGNET- (NEGATIVECURRENT) CLL COIL FLUX /N AMPERE- TURNS /Nl/E/VTOR @y 6.5. PERREAULT Wm7% 7&6@

ATTORNEY United States Patent G 3,015,707 RELAY George E. Perreault,White Plains, NX., assigner to Bell Telephone Laboratories,incorporated, N ew York, NX., a corporation of New York Filed Nov. 19,1957, Ser. No. 697,465 9 (Ilaims. (Cl. 20G-87) This invention relates torelays, and more particularly to magnetically latched relays.

There has been developed a glass-sealed reed device which acts as thecontact means for a relay. This reed device is generally placed axiallyWithin the energizing coil of the relay where it becomes extremely rapidin action and very sensitive. Such device is disclosed in Patent2,289,830, granted to W. B. Ellwood, July 14, 1942; and, it has beenemployed in numerous combinations, one of which showing sequentialoperation of a plurality of such contact devices is set forth in Patent2,243,399, granted to A. M. Skellett, May 24, 1941.

The glass-sealed reed device is of relatively simple constructionconsisting essentially of two reeds which are mounted at opposite endsof an elongated glass envelope. In addition to protecting the 'reedcontacts from dirt and the like, this construction results in extremelylow unit cost and this, in turn, accounts in large measure for theextensive use that has been accorded the device.

It is an object of this invention to simplify the structure ofmagnetically latched relays through the use of glass-sealed reeddevices.

-It is a further object of this invention to reduce the cost and toincrease the utility and the reliability of magnetically latched relays.

These andother objects are attained in accordance with the presentinvention wherein four glass-sealed reed devices are grouped together sothat, the glass envelopes being cylindrical, a void space exists .in thecenter f the group. A permanent magnet of relatively short length isplaced in this space at a position adjacent the switch gaps of thereeds. The permanent magnet thus provides a latching function for allfour reed devices. A common coil surrounds the group and serves tosimultaneously energize the reeds to control electrical circuits.

Other objects and many of the attendant advantages of the invention willbe readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings in which:

FIG. l is an enlarged longitudinal view, partially in cross section, ofa device constructed in accordance with the present invention;

FIG. 2 is an enlarged view taken on the line 2 2 of FIG. l; and

FIG. 3 is a series of curves useful in explaining a feature of thepresent invention.

As the name implies, a magnetically latched relay is one which can beheld or latched in the operated state. This is accomplished through theuse of a permanent magnet that is adiusted to provide enough magneticflux to keep closed switch contacts closed, but not enough flux to closeswitch contacts that are open. The coil Which is associated with therelay provides the balance of flux required to change the relay from theopen to the closed state. The obvious advantage of a magneticallylatched relay is that no power is required to maintain the relay ineither the operated or unoperated condition.

With this brief summary of operation in mind, reference should now behad to FIGS. l and 2 of the drawings wherein four glass-sealed reeddevices 11 are grouped together. The switch contacts of each reed deviceare en closed in a hermetically sealed, tubular envelope 12 made of avitreous material such as glass. An inert gas such 3,0l5,707 PatentedJan. 2, 1952 HCC as helium, argon, neon, or any other non-corrosive gas,may be inserted in this enclosure for the purpose of reducing arcingacross the contact gap, but this is in no way essential for successfuloperation of the present invention. Inserted and sealed in each envelopeat either end thereof are contact reeds 13 and 14 having overlappingcontact areas 15 and 16, respectively. These contact reeds may be formedof any suitable magnetic material of high electrical conductivity. Asshown more clearly in FIG. 2, the contact reeds 13 and 14 are made froma flat member, but it will be readily appreciated that round Contactmembers or members of other cross sectional conguration may be readilysubstituted for the reeds 13 and 14 without departing from the spirit orscope of the invention. Contact areas l5 and 16 may be plated with goldor other precious metal Ito improve the over-all operatingcharacteristics of the device.

The four reed devi-ces 11 are coextensive and so grouped that, the glassenvelopes being cylindrical, a void space exists in the center of thegroup. A permanent magnet 17 of relatively short length is placed inthis space and at such a position that it straddles each of the switchgaps. Thus, the single permanent magnet provides the latching functionfor all four reed devices. With the permanent magnet 17 so positioned,maximum flux can be concentrated at the gaps. And, as will be describedin detail below, this close association of the permanent magnet tlux tothe switch gaps results in a much greater margin against false operationthan has heretofore been obtained by other arrangements.

lt should be clear at this point that the permanent magnet could in factbe utilized in combination with other groupings of reed devices. Forexample, ve or more reed devices might be arranged in a tight groupingwith the permanent magnet disposed in the center thereof. There are,however, advantages in the disclosed arrangement. With the reed devicesgrouped as shown, so that they are close to touching, the permanentmagnet can be placed in the void space formed by the tangency of thefour devices and thus a magnetically latched relay can be provided whichoccupies no greater space than a neutral relay having the equivalentnumber of switching units. In addition, by lling the void space with asquare cross section magnet a near maximum volume of magnetic materialcan be located adjacent the switch gaps.

A common coil surrounds the entire group and serves to simultaneouslyenergize the reeds to control electrical circuits. A metallic casing 19of magnetic material provides a return path of low reluctance for thecoil ux.

The action of the relay can be visualized by considering the directionsof the magnetic fields produced by the permanent magnet and the coil. Aninitially open switch is, of course, subject to the inuence of thepermanent magnet, but the force is not high enough to close the switchcontacts. If, however, a pulse of current is sent through the coil whichsets up a flux in the same direction as the ilux from the permanentmagnet, the contacts will close. The permanent magnet then keeps themclosed with no further current required in the coil. To open thecontacts, a second pulse of current is sent through the coil in theopposite direction and it produces a ux that opposes and overcomes thepermanent magnet flux thus releasing the reeds.

Another way of describing relays of this type is to consider theiroperating characteristics. Turning to the curves of FIG. 3 and assumingiirst the absence of the permanent magnet, there are four sensitivitypoints of operation for any group of relays under test. The point Aindicates the point at which the coil flux is suicient to insure theoperation` of all the relays. The point B indicates the point at whichall the relays fail to operate.

Between points A and B some, but not all of the relays may operate. And,now assuming all relay contacts have been closed, the point C indicatesthe point to which the coil ux can be reduced withA all the contactscontinuing to hold or remain closed. Finally, the point D is the pointat which all relay contacts release. With negative current or current inthe reverse direction applied tol the coil, the relays exhibit a mirrorimage (A, B', C', D) of these four sensitivity points.

For a magnetically latched relay, the permanent magnet shifts thesesensitivity points as shown in FIG. 3. This shifting of the sensitivitypoints from A, B to a, b, for example, is due to the fact that thepermanent magnet acts in combination with the coil to supply the totalflux necessary to operate the relay contacts. Thus, with the coil fluxacting in the same direction (positive current) as the permanent magnetlux, substantially less current is required to actuate or close allcontacts. It will be noted that the hold point C is shifted to point c,the eliect of this being that once the relay switch contacts are closedcoil flux can be reduced to zero and the contacts will remain closed. Toopen the contacts it is necessary to apply current in the oppositedirection (negative direction) to the coil.

A magnetically latched relay must have good margins against thenonoperate (point b) and hold (point c) conditions at zero coil linx.This is to prevent the switches from falsely operating or releasing whenthe relay is subjected to shock, vibration or stray elds. To this endthe permanent magnet is adjusted so that the points b and c straddle thepoint of zero coil flux.

From the above it will thus be seen that a magnetically latched relaywill operate on less coil ux than a relay without a permanent magnet,will remain operated on zero coil ilux, will release on a negative coilux, and will then stay released with zero coil flux. Further, such arelay may be used either as a normally closed relay or as a normallyopen one.

AsV indicated, to open closed contactsit is necessary to send a pulse ofcurrent through the coil (negative direction) which will oppose andovercome the permanent magnet ux. With regard to FIG. 3, this currentpulse must provide a coil flux (ampere-turns) which equals or exceedsthat of release point d. Unfortunately, however, if this coil fluxbecomes too large the contacts will reclose and this is known, in theart, as false operation.

ShouldV the pulse of negative current produce a coil flux which equalsor exceeds that at false operate point a', the contacts would eitherremain closed or momentarily open and then reclose. Upon termination ofthe pulse, the permanent magnet would, of course, keep the contactsclosed.

If the contacts are assumed closed and the coil liux is slowly increasedin the negative direction from zero, all the contacts would open betweenthe points c and d and they would remain open until point b was reached,at which time a first set of contacts would close. However, for manyapplications relay coils are necessarily pulse operated. And, when thepulse of negative current produces a ux which exceeds the false holdpoint c the contacts do not open but rather are held closed. That is,the coil flux reaches the value c so rapidly that the contacts do nothave time to open. Thus, the contacts are falsely held and will remainso upon termination of the pulse due to the held of the permanentmagnet. The same result occurs between the points d'-c except that inthis region some of the contacts doin fact open while others remainclosed.

I f it were possible to always pulse operate the relays s that only apreselected amount of coil ilux would be produced, false operation wouldnot be encountered. However, changes in the supply voltage and/ orambient temperature can have substantial eiiects on the flux produced.For example, temperature changes can result in as much as a twenty-fivepercent variation in the overall resistance of the coil and this,ofcourse, affects a correspending variation in coil current and hence coilflux..

By making the false operate-,points (a, b', c', d') occur atincreasingly higher values of coil llux (such as points a, b", c, d),increased insurance against false operation can be obtained. That is, byspreading these false operate points as far as possible from the usableoperating points (c, d) the relays will be more reliable in use. It hasbeen found that this can be achieved through the proper selection andplacing of the permanent magnet. Specically, a permanent magnet isutilized which is very short relative to the length of the coil and itis positioned as disclosed. Tests have shown that, under everydayoperating conditions, this false operate problem can be substantiallyeliminated by using apermanent magnet having a length which isone-quarter or less the length of the coil. Stated somewhat diiierently,the ratio of coil length/permanent magnet length should be of the orderof four or more and the higher this ratio the better. Since the coilsize is generally set by space considerations, this length relationshipwill be arrived at in most cases by selectingV a suliiciently shortpermanent magnet. However, the permanent magnet must always comprisesufficient material so as to carry out its intended function, namely,holding closed switch contacts closed.

The dotted curves of FIG. 3 illustrate the eiective displacement of thefalse operate points, from d', c to d", c", for example. These curveswere obtained for a relay, constructed in accordance with the presentinvention, wherein the permanent magnet was one-quarter the length ofthe coil and was positioned adjacent the switch gaps as.

shown in FIG. l.

A physical explanation ofthis false operate point displacement may bearrived at by considering the respective flux paths in one of the reeddevices. With the switch contacts closed` and the magnet 17 positionedas shown in FG. l, the permanent magnet ux can be assumed to enter thereed 13, travel toward and through the abutting Contact areas 15 and 16,then alongthe reed 14, and finally across the air gapto the oppositepole. To open the contacts, the coil flux must travel through the reedsin the opposite direction (from reed 14 to 13) and must be of sufficient`intensity to overcome `the permanent magnet flux therein. Withincreasing values of coil ilux (negative direction) the overcoming ofthe permanent magnet ilux will be accompanied by approaching saturationof the reed material in those regions of the reeds where the coil iluxis unopposed. That is, in trying to get enough coil flux down the reedsso as to overcome the permanent magnet liux concentrated near the switchgap, the reed material in the said unopposed regions begins to saturate.Increasing the coil llux further, of course, results in a furtherapproach to saturation which in turn results in decreased permeabilityof the material. The reed material near the switch gap does not saturatebecause here they respective fluxes tend to cancel each other out.

Now by increasing the length of travel of the coil ilux. in the reedswith respect to that of the permanent magnet ilux, this eieot can besubstantially enhanced. The resultsl of such an increase is a cumulativeone, for the added length of saturable material means that increasedcoil iiux will be needed to produce a desired eiect at the switch gap.However, increased coil ilux will cause `an even closer approach tosaturation which in turn will lower even further the permeability of thereed material. AS will be realized, this relative increase in the coiliiux path length is accomplished by increasing the relative length or"the coil with respect to the permanentmagnet.

Turning to the curves of FIG. 3, `and assuming for the moment ythat itis desired to reclose all previously closed contacts, it would normally`be necessary that the coil ux be of a value (negative direction) equalto that of point a'. However, with added saturable material in the coillinxr path more coil flux is necessary to produce this desideratum,i.e., false reelosure. This added coil flux will, of course, furtherdecrease the permeability of the reed material making it necessary toresort `to still more coil fiux. Of course, false reclosure is notdesired, but the above discussion is still valid. Thus, by increasingthe coil flux path length the `false operate point a', as well as theothers, can be effectively displaced.

While the length of the coil to the permanent magnet is not extremelycritical, effective displacement of the false operate points is obtainedwhen the coil length iS at least four times that of the magnet, orconversely when the magnet is no more than one-quarter the length of thecoil. Further, it is desirable to position the permanent magnet 17 sothat it straddles the switch gaps. In this manner maximum flux can beconcentrated at the gaps and the permanent magnet flux path through thereeds is kept to a minimum. If the permanent magnet were placed adjacentone of the ends of the reed devices, for example, its flux path in thereeds would be just about the same as the coil flux path. And this wouldtend to cancel the effect discussed above with the result that therecould be no effective displacement of the false oper-ate points,

One rather obvious modification of the above-described arrangement would-be to combine two or more groups of magnetically controlled switches in-a single coil. A further modification of this would be to then positionthe permanent magnet of one group with a polarity the reverse of theother groups. This would provide a relay with some normally closedcontacts and some normally open contacts. A current puise through thecoil would then serve to reverse these conditions.

It is to be understood that the above-described arrangements are merelyillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

l. In a magnetically latched relay, ra plurality of reed switchingdevices arranged in la group, each of said switching devices comprisinga tubular envelope and a pair of contact reeds mounted at respectiveends of said envelope and extending longitudinally thereof `so as topresent overlapping contact areas, a short permanent magnet disposedcentrally of said group of switching devices at a position adjacent theswitch gaps thereof, `and a common energizing coil surrounding saidgroup; the magnet providing a magnetic flux for magnetizing saidoverlapping contact areas only.

2. In a magnetically latched relay, a plurality of reed switchingdevices arranged coextensively in a group, each of said switchingdevices comprising a tubular envelope and a pair of contact reedsmounted at respective ends of said envelope and extending longitudinallythereof so as to present overlapping contact areas, a permanent magnetdisposed in the center of said group of switching devices and at alongitudinal position which is symmetrical with respect to the switchgaps thereof, and a common energizing coil surrounding said group, saidpermanent magnet being short with respect to the length of said coil andproviding a magnetic flux lfor magnetizing said overlapping contactareas only.

3. A magnetically latched relay comprising four reed switching devicesyarranged ycoextensively in a group, each of said switching -devicescomprising a tubular envelope and a pair of contact reeds mounted atrespective ends of said envelope and extending longitudinally ythereofso as to present overlapping contact areas, said switching devices beinggrouped so that, the tubular envelopes being cylindrical, a void spaceexists in the center of the group, a short permanent magnet disposed insaid void space at a longitudinal position which is symmetrical withrespect to the switch gaps of said switching devices, and a commonenergizing coil surrounding said group; the magnet providing a magneticux for magnetizing said overlapping contact areas only.

4. In a magnetically latched relay, a plurality of reed switchingdevices arranged coextensively in a group, each of said switchingdevices comprising a tubular envelope and a pair of contact reedsmounted at respective ends of said envelope and extending longitudinallythereof so as to present overlapping contact areas, a short permanentmagnet disposed in the center of said group of switching devices and yata longitudinal position which is symmetrical with respect to the switchgaps thereof, and a common energizing coil surrounding said group, saidpermanent magnet being no -longer than one-quarter the length of saidcoil and providing a magnetic flux for magnetizing said overlappingcontact areas only.

5. A magnetically latched relay comprising four reed switching devicesarranged coextensively in a group, each of said switching devicescomprising `a tubular envelope and a pair of contact reeds mounted atrespective ends of said envelope and extending longitudinally thereof soas to present overlapping contact areas, said switching devices beinggrouped `so that, the tubular envelopes being cylindrical, a void spaceexists in the center of the group, a short permanent magnet disposed insaid void space at a longitudinal position which is symmetrical withrespect to the switch gaps of said switching devices, and a commonenergizing coil surrounding said group, said permanent magnet being nolonger than one-quarter the length of said coil and providing a magneticflux for magnetizing said overlapping contact areas only.

6. A relay comprising a plurality of reed switching devices arranged ina group, each switching device including a pair of magneticallydeilectable reeds sealed wi-thin a non-magnetizable tubular envelope`and protruding, respectively, through opposing ends of the envelope,each said pair of reeds -being arranged within the envelope so that onereeds end portion is separated from, and overlaps, the other reeds endportion lthereby defining a gap between the one reeds end portion andthe other reeds end portion whereby each of the switching devices is inan open state, a coil surrounding said group of switching devices forproducing, upon energization, la first magnetic flux for deflecting eachpair of reeds so that the overlapping end portions thereof are broughtinto mutual contact whereby each of the Switching devices is caused tochange from said open state to `a closed state, and a permanent magnetcontinuously producing a second magnetic fiux for magnetizing theoverlapping end portions only of each switching devices pair of reedsand maintaining each of the switching devices in the closed statesubsequent to the deenergization of the coil.

7. A relay, as is defined in claim 6, wherein said permanent magnet isnot `longer than one-fourth of the coils length.

8. A relay comprising a plurality of reed switching devices arranged ina group, each switching device including a pair of magneticallydeiiectable reeds sealed wi-thin -a non-magnetizable tubular envelopeand protruding, respectively, through opposing ends of said envelope,each said pair of reeds being arranged within the envelope so that onereeds end portion is separated from, and overlaps, the other reeds endportion thereby defining a gap between the end portions of lsaid onereed and said other reed whereby each said switching -device is in anopen State, a coil surrounding said group of switching devices, saidcoil being susceptible of being energized, selectively, to produceeither a first magnetic field or a second magnetic field, said secondmagnetic field, lbeing oriented oppositely of said first magnetic field,said first magnetic field causing each said pair of reeds to deflect sothat their overlapping end portions move into mutual contact wherebyeach of the switching devices is changed from said open state to aclosed state, and ya permanent magnet continuously producing a thirdmagnetic field, oriented in the same direction as the first magneticfield, for magnetizing said overlapping end portions only of each saidpair of reeds thereby maintaining each of the switching devices in theclosed state subsequent to deenergization of said coil; said secondmagnetic field causing each of the switching devices to return to theopen state from the closed state in which they are being maintained.

length.

References Cited in the le of this patent UNITED STATES PATENTS DroysenApr. 10, 1934 Ellwood et al ...,T- Jan. 16, 1940 8 Ellwood July 14, 1942Dichten June26, l1945' Brown Mar. 26, 1946 O-Neill Aug. 14, 1956 OliverMair. 10, 1959 Peek Mar. 10, 1959 Wilhelm Oct. 6, 1959 Mol-yneaux Dec.9, 1959

